This disclosure is based on application No. H10-373630 filed in Japan on Dec. 28, 1998, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a taking lens system, and more particularly to a compact taking lens system suitable for use in a digital input apparatus such as a digital still camera or digital video camera.
2. Description of the Prior Art
In recent years, as personal computers become prevalent, digital still cameras, digital video cameras, and the like (hereafter referred to simply as digital cameras) that allow easy storage of image data in a digital format have become more popular for personal use. Such digital cameras are expected to become more widespread as an apparatus for inputting image data.
On the other hand, such digital cameras have come to employ smaller and smaller solid-state imaging devices, for example, CCDs (charge-coupled devices), and therefore digital cameras themselves are quite naturally expected to be made more compact. Consequently, further miniaturization is eagerly sought in taking lens systems, because they occupy the largest space within digital input devices.
To cope with such requirements, for example, Japanese Laid-open Patent Application No. H9-166748 proposes a compact taking lens system suitable for use in a camera having a CCD that is composed of as few constituent lens elements as possible. In this proposed arrangement, however, the taking lens system has a negative-positive-positive lens arrangement on the rear (image) side of its aperture stop. In a taking lens system of this type, convex lens elements are located in a rear portion thereof, and therefore it is difficult to secure a sufficient edge margin in the convex lens elements. This makes it difficult to achieve further miniaturization of the entire taking lens system. In this context, the edge margin of a lens element refers to the portion of the lens element that falls outside its effective diameter.
An object of the present invention is to provide a compact taking lens system that offers sufficiently high optical performance. To achieve this object, according to one aspect of the present invention, a taking lens system is provided with, from the object side, a first negative lens element, a second biconvex lens element, an aperture stop, a third positive lens element, a fourth negative lens element, and a fifth positive lens element. In the taking lens system, the following condition is fulfilled:
xe2x88x920.99 less than (r21+r22)/(r21xe2x88x92r22) less than 0.56
where
r21 represents the radius of curvature of the object-side surface of the second lens element; and
r22 represents the radius of curvature of the image-side surface of the second lens element.
According to another aspect of the present invention, a taking lens system is provided with, from the object side, a first biconcave lens element, a second positive lens element, an aperture stop, a third positive lens element, a fourth negative lens element, and a fifth positive lens element. In the taking lens system, the following condition is fulfilled:
0.12 less than n2xe2x88x92n1 less than 0.39
where
n1 represents the refractive index of the first lens element for the d line; and
n2 represents the refractive index of the second lens element for the d line.
According to another aspect of the present invention, a taking lens system is provided with, from the object side, a first negative lens element, a second positive lens element, an aperture stop, a third positive lens element, a fourth negative lens element, and a fifth positive lens element. The third and fourth lens elements are cemented together. In the taking lens system, the following condition is fulfilled:
xe2x88x920.02 less than F/F34 less than 0.18
where
F represents the focal length of the entire taking lens system; and
F34 represents the focal length of the doublet lens element formed by cementing together the third and fourth lens elements.
According to another aspect of the present invention, a taking lens system is provided with, from the object side, a first negative lens element, a second biconvex lens element, an aperture stop, a third positive lens element, a fourth negative lens element, and a fifth positive lens element. The third and fourth lens elements are cemented together. In the taking lens system, the following condition is fulfilled:
0.3 less than F/F345 less than 0.9
where
F represents the focal length of the entire taking lens system; and
F345 represents the composite focal length of the third to fifth lens elements.
According to still another aspect of the present invention, a taking lens system is provided with, from the object side, a first negative lens element, a second biconvex lens element, an aperture stop, a third positive meniscus lens element convex to the image side, a fourth negative lens element, and a fifth positive lens element. The fourth and fifth lens elements are cemented together. In the taking lens system, the following condition is fulfilled:
0.3 less than F/F345 less than 0.9
where
F represents the focal length of the entire taking lens system; and
F345 represents the composite focal length of the third to fifth lens elements.